let canvas, ctx, w, h, hue, stars, count, maxStars
let canvas2, ctx2
let half, gradient2

function init(elCanvas) {
  canvas = elCanvas
  ctx = canvas.getContext('2d')
  w = canvas.width = window.innerWidth
  h = canvas.height = window.innerHeight
  hue = 217
  stars = []
  count = 0
  maxStars = 1200

  canvas2 = document.createElement('canvas')
  ctx2 = canvas2.getContext('2d')
  canvas2.width = 100
  canvas2.height = 100
  half = canvas2.width / 2
  gradient2 = ctx2.createRadialGradient(half, half, 0, half, half, half)
  gradient2.addColorStop(0.025, '#fff')
  gradient2.addColorStop(0.1, 'hsl(' + hue + ', 61%, 33%)')
  gradient2.addColorStop(0.25, 'hsl(' + hue + ', 64%, 6%)')
  gradient2.addColorStop(1, 'transparent')

  ctx2.fillStyle = gradient2
  ctx2.beginPath()
  ctx2.arc(half, half, half, 0, Math.PI * 2)
  ctx2.fill()

  for (let i = 0; i < maxStars; i++) {
    new Star()
  }
}
// End cache

function random(min, max) {
  if (arguments.length < 2) {
    max = min
    min = 0
  }

  if (min > max) {
    let hold = max
    max = min
    min = hold
  }

  return Math.floor(Math.random() * (max - min + 1)) + min
}

function maxOrbit(x, y) {
  let max = Math.max(x, y),
    diameter = Math.round(Math.sqrt(max * max + max * max))
  return diameter / 2
}

let Star = function () {
  this.orbitRadius = random(maxOrbit(w, h))
  this.radius = random(60, this.orbitRadius) / 12
  this.orbitX = w / 2
  this.orbitY = h / 2
  this.timePassed = random(0, maxStars)
  this.speed = random(this.orbitRadius) / 900000
  this.alpha = random(2, 10) / 10

  count++
  stars[count] = this
}

Star.prototype.draw = function () {
  let x = Math.sin(this.timePassed) * this.orbitRadius + this.orbitX,
    y = Math.cos(this.timePassed) * this.orbitRadius + this.orbitY,
    twinkle = random(10)

  if (twinkle === 1 && this.alpha > 0) {
    this.alpha -= 0.05
  } else if (twinkle === 2 && this.alpha < 1) {
    this.alpha += 0.05
  }

  ctx.globalAlpha = this.alpha
  ctx.drawImage(canvas2, x - this.radius / 2, y - this.radius / 2, this.radius, this.radius)
  this.timePassed += this.speed
}

function animation() {
  ctx.globalCompositeOperation = 'source-over'
  ctx.globalAlpha = 0.8
  ctx.fillStyle = 'hsla(' + hue + ', 64%, 6%, 1)'
  ctx.fillRect(0, 0, w, h)
  ctx.globalCompositeOperation = 'lighter'
  for (let i = 1, l = stars.length; i < l; i++) {
    stars[i].draw()
  }

  window.requestAnimationFrame(animation)
}

let huhuiyu = {
  startAnimate(el) {
    el.innerHTML = ''
    let elCanvas = document.createElement('canvas')
    el.appendChild(elCanvas)
    huhuiyu.el = elCanvas
    init(elCanvas)
    animation()
    return elCanvas
  },
}

export default huhuiyu
